NEW U PU METALLIC SPIKES FOR SAFEGUARDS ACCOUNTANCY MEASUREMENTS AT REPROCESSING PLANTS/

A new generation of metallic uranium/plutonium spikes has been develop ed for U and Pu determinations in undiluted input solutions of reproce ssing plants. The Pu spike is in the form of a Gd-6% Pu-0.16% Nd (mass %) alloy disc prepared by levitation melting. The Gd provides a ductil e matrix in which the Pu is present in solid solution. The alloy has g ood oxidation resistance, but is readily soluble in the nitric acid me dium of the input solution. The Nd addition is to permit a determinati on of input tank volume via the measurement of Nd-142/143 ratios. The U spike is a metal disc with U-235 enrichment of 19.9 amount%. A gamma -counting method of plutonium homogeneity control was developed using a Monte-Carlo simulation to correct for gamma-ray self-absorption. The spikes were certified for uranium and plutonium mass fractions and am ount ratios as Isotopic Reference Material (Spike) IRMM-1030.